WO2021107277A1

WO2021107277A1 - Feco nanochain, method of preparing same, and electromagnetic wave-absorbing body

Info

Publication number: WO2021107277A1
Application number: PCT/KR2020/002922
Authority: WO
Inventors: 정재원; 박병진; 양상선; 이상복
Original assignee: 한국재료연구원
Priority date: 2019-11-28
Filing date: 2020-02-28
Publication date: 2021-06-03
Also published as: KR20210066958A

Abstract

The object of the present invention is to provide a FeCo nanochain in which a plurality of nanoparticles are fused to one another on the surfaces thereof to form a one-dimensional linear structure; a method of preparing same; and an electromagnetic wave-absorbing body comprising same. To this end, the present invention provides a FeCo nanochain characterized in that a plurality of nanoparticles are fused to one another on the surfaces thereof to form a one-dimensional linear structure, each nanoparticle having a diameter of 30 nm to 500 nm. In addition, the present invention provides a method of preparing the FeCo nanochain having a one-dimensional linear structure. In addition, the present invention provides an electromagnetic wave-absorbing body comprising the FeCo nanochain in which a plurality of nanoparticles are fused to one another on the surfaces thereof to form a one-dimensional linear structure, each nanoparticle having a diameter of 30 nm to 500 nm. According to the present invention, it is possible to provide a magnetic material having a high permeability in a high frequency range and prepare the magnetic material by a simple method, and when the magnetic material is applied to an electromagnetic wave-absorbing body, desirable effects may be obtained.

Description

FECO nano chain, manufacturing method thereof, and electromagnetic wave absorber including same

The present invention relates to a FeCo nanochain, a method for manufacturing the same, and an electromagnetic wave absorber including the same.

With the remarkable development of the electrical and electronic parts industry and the telecommunication industry, it is contributing a lot to homes, industrial sites, and military weapon systems. As these electrical and electronic parts are miniaturized, low-power, and highly integrated, equipment malfunctions and functional deterioration due to weakened immunity to electromagnetic waves. is occurring a lot.

In addition, research on protection facilities to protect against high-power electromagnetic waves (EMP, HPM) of tactical command and control system (C4I) facilities related to national security and investment in protection facilities at the national level are being carried out in the mid- to long-term. The core part of the electromagnetic wave absorber (or shielding) function to protect electronic equipment is absolutely necessary.

These electromagnetic wave absorbers are widely used in electromagnetic wave compatibility (EMC) and antenna electromagnetic wave measurement facilities for precise and reliable electromagnetic wave measurement in the industrial field, and in the field of military-related weapon systems, stealth (RCS) It is used to reduce unnecessary electromagnetic waves so that they are not radiated around the function and high-power electromagnetic wave radiation equipment.

When an electromagnetic wave is incident from the outside, a general electromagnetic wave absorber converts unnecessary electromagnetic wave energy into thermal energy to extinguish it. For example, an electromagnetic wave absorber using magnetic materials, when incident waves are incident from the outside, reflects unnecessary reflected waves at the interface and converts unnecessary electromagnetic wave energy into thermal energy from the inside. It is destroyed by heat conversion, and the required electromagnetic waves (Transmitted waves) are transmitted. As another example, the electromagnetic wave absorber using a shielding material uses a conductive material such as metal to convert unnecessary electromagnetic waves incident from the outside into high-frequency currents to shield electromagnetic interference. Among the performance of the electromagnetic wave absorber, the most important characteristic is the electromagnetic wave absorption ability, and the material and shape of the electromagnetic wave absorber are different for each frequency band.

According to the method of converting electromagnetic waves into thermal energy, electromagnetic wave absorbers are broadly classified into three types: magnetic absorbers, dielectric absorbers, and conductive absorbers. Among them, ferrite, which is a magnetic absorber, has a flat plate structure and has high absorption and durability. In addition, while it has the advantage of tolerating heat, the installation cost is high and the width of the absorption area is limited.

For example, the electromagnetic wave absorber used in the low band of about 30 MHz to 1 GHz is composed of a plate-shaped ferrite panel absorber. These ferrites are representative magnetic loss materials. Mn-Zn ferrite and Ni-Zn ferrite, which are soft magnetic ferrites, have high magnetic losses that affect their ability to absorb electromagnetic waves, but their magnetic losses sharply decrease in the GHz band. It does not function as a good electromagnetic wave absorber. Accordingly, the electromagnetic wave absorber used in the high band of 1 GHz to 40 GHz or more is formed in the structure of a pyramid-shaped absorber containing carbon fibers.

In addition, the electromagnetic wave absorber used in the broadband of 30 MHz to 40 GHz or higher is provided in a complex structure in which the absorber is combined in a pyramid shape including carbon fibers on the upper part of the ferrite panel absorber used in the low band.

The pyramid-shaped absorber used as such an existing broadband frequency absorber is produced by impregnating polyurethane foam with a carbon powder solution to form a surface coating, followed by molding.

However, these conventional electromagnetic wave absorbers are harmful to the human body by generating dust that causes respiratory and cancer diseases, and the cost of disposing of existing products according to a short life cycle occurs, and adversely affects environmental pollution.

Accordingly, there is a growing demand for an electromagnetic wave absorber that overcomes the problems of the conventional electromagnetic wave absorber, reduces the harmfulness of the human body due to dust generation, and improves durability by improving the physical properties of the electromagnetic wave absorber.

For example, Korean Patent Laid-Open No. 10-2018-0084351 discloses an invention related to a polymer-based broadband electromagnetic wave shielding film, specifically comprising a polymer and a filler dispersed in the polymer, wherein the filler is multilayer graphene; nanotubes positioned between or on the surface of the multilayer graphene and connected to the graphene; and a nanostructure including a metal oxide connected to the nanotube, an electromagnetic wave shielding film is disclosed. However, the above technology has problems in that the process for manufacturing a filler is not simple, it is difficult to manufacture a filler of a desired standard, and furthermore, it is difficult to uniformly disperse the filler in the polymer.

Accordingly, the inventors of the present invention have led to the present invention by studying FeCo nanochains that can be simply manufactured, particularly FeCo nanochains that can be used as an electromagnetic wave absorber, and a manufacturing method thereof.

An object of the present invention is to provide a FeCo nano-chain in which a plurality of nanoparticles are fused to each other on a particle surface to form a one-dimensional linear structure, a method for manufacturing the same, and an electromagnetic wave absorber including the same.

To this end, the present invention

A plurality of nanoparticles are fused to each other on the particle surface to form a one-dimensional linear structure, and each nanoparticle has a diameter of 30 nm to 500 nm.

Also, the present invention

introducing a mixed powder of iron and cobalt or an alloy powder of iron and cobalt into the plasma region; and

It provides a method for manufacturing a one-dimensional linear structure of FeCo nanochains comprising the; forming FeCo nanochains through thermal plasma synthesis.

Furthermore, the present invention

A plurality of nanoparticles are fused to each other on the particle surface to form a one-dimensional linear structure, and each nanoparticle has a diameter of 30 nm to 500 nm to provide an electromagnetic wave absorber including FeCo nanochains.

According to the present invention, a magnetic material having high permeability in a high frequency band can be provided, and it can be manufactured by a simple method, and when applied to an electromagnetic wave absorber, excellent effects can be obtained.

1 is a schematic diagram showing a one-dimensional linear structure of a FeCo nanochain according to the present invention,

2 is a SEM photograph of a structure manufactured when only iron is used as a raw material and when iron and cobalt are used as raw materials;

3 is a TEM photograph of the FeCo nanochain prepared by the manufacturing method of the present invention;

4 is an SEM photograph of FeCo nanochains prepared according to the composition ratio;

5 is a graph showing the dielectric constant and permeability of the FeCo nanochain of the present invention,

6 is a graph comparing the dielectric constant and permeability of the FeCo nanochain of the present invention and known materials,

7 is a TEM photograph in which a silica coating layer is formed on the surface of the FeCo nanochain of the present invention, and

8 to 11 are graphs of experimental results that can confirm the performance of the electromagnetic wave absorber including the FeCo nanochain of the present invention,

The present invention provides a FeCo nanochain characterized in that a plurality of nanoparticles are fused to each other on the particle surface to form a one-dimensional linear structure, and each nanoparticle has a diameter of 30 nm to 500 nm.

The FeCo nanochain of the present invention is a FeCo nanochain that forms a one-dimensional linear structure as a plurality of nanoparticles are fused on the particle surface through mutual collision during the manufacturing process, and each nanoparticle diameter is 30 nm to 500 It is characterized in that it is nm. Since the FeCo nanochain of the present invention has a one-dimensional linear structure, it has shape magnetic anisotropy, which has the effect of improving the magnetic resonance frequency compared to the spherical particles. As the magnetic resonance frequency is improved, high permeability can be exhibited compared to spherical particles even in high frequency bands (several GHz or more), and as a result, electromagnetic wave absorption characteristics can be improved at high frequencies.

In addition, when the diameter of each of the nanoparticles of the FeCo nanochain of the present invention is less than 30 nm, the particle radius is too small and the surface area to volume is high, so the weight ratio of the particles that can be contained per unit volume is very small, so the electromagnetic wave absorption characteristics are small If the diameter exceeds 500 nm, there is a problem in that it is difficult to separate from the non-reacted micropowder in the thermal plasma method synthesis process because the particles are heavy.

At this time, it is preferable that the aspect ratio of the FeCo nanochain of the present invention is 1.5 to 15. If the aspect ratio is less than 1.5, there is a problem in that the magnetic permeability is insignificant due to low shape magnetic anisotropy, and when it exceeds 15, there is a problem in that the dielectric constant is excessively high because the particles have excessively high electronic conductivity in the particles.

It is preferable that the FeCo nanochain according to the present invention further comprises a dielectric inorganic coating on the surface. The nanochain according to the present invention can control the dielectric constant by further including a dielectric inorganic coating on the surface, and ultimately, when the FeCo nanochain according to the present invention is used as a configuration of an electromagnetic wave absorber, excellent absorption performance in a broad band is obtained. There is an effect that can be exerted.

The dielectric inorganic coating may be a coating of various components, but in the case of silica, since TEOS obtained as a by-product in the silicone resin manufacturing process is used as a raw material, it has the advantage of being inexpensive and easy to use in the process. In addition, silica coating is preferable in that a high-performance composite having various material functions can be obtained by mixing various types of metal alkoxides during the coating process. However, the dielectric inorganic coating is not limited to silica, and various inorganic coatings having insulating properties and dielectric properties can be applied. (eg TiO2, Al2O3, ZnO, etc.)

The thickness of the inorganic dielectric coating coated on the FeCo nanochain of the present invention is preferably 2 nm to 200 nm. The dielectric inorganic coating controls the dielectric constant and ultimately, when the FeCo nanochain according to the present invention is used as the composition of the electromagnetic wave absorber, in that it enables excellent absorption performance in a broad band, when the thickness is less than 2 nm, the dielectric constant control There is a problem that cannot be sufficiently performed, and when the thickness exceeds 200 nm, the dielectric constant becomes excessively high due to a thick coating layer, thereby lowering the electromagnetic wave absorption characteristics.

The FeCo nanochain of the present invention can be used as an electromagnetic wave absorber. In order to have a high magnetic permeability of 1 or more at the corresponding frequency, the magnetic particles for electromagnetic wave absorbers in the tens to tens of GHz band should have a one-dimensional or two-dimensional shape anisotropy rather than a spherical structure, and also have high saturation magnetization according to Sneok's limit. FeCo has a saturation magnetization of 2.45T when Fe is 65wt%, indicating the highest saturation magnetization value among materials known to date. The nanochain structure has a high aspect ratio, so the magnetic resonance frequency is higher than that of spherical particles due to shape magnetic anisotropy. high and consequently high permeability at high frequencies. The FeCo nanochain structure of the present invention has a high saturation magnetization value of 2.3 T or more based on the FeCo composition, and at the same time has a nanochain structure, so it has a high resonance frequency due to shape magnetic anisotropy. have Therefore, it is very suitable as a material as a filler for electromagnetic wave absorbers applicable in a band of several to several tens of GHz.

Also, the present invention

Hereinafter, the manufacturing method of the present invention will be described in detail for each step.

The manufacturing method of the present invention includes introducing a mixed powder of iron and cobalt or an alloy powder of iron and cobalt into a plasma region. A mixed powder of iron and cobalt or an alloy powder of iron and cobalt is a raw material for FeCo nanochains, and when they are introduced into the plasma region, a one-dimensional linear structure is formed through collision and fusion processes. However, a one-dimensional linear structure is formed only when iron and cobalt components are introduced into the plasma region together. For example, when only iron is introduced into the plasma region, a spherical structure is formed instead of a one-dimensional linear structure of iron. .

The manufacturing method of the present invention is a step in which the raw materials introduced into the plasma region form FeCo nanochains through a thermal plasma synthesis method. Since the thermal plasma synthesis method is a known technique, a detailed description thereof will be omitted. However, in this case, in the manufacturing method of the present invention, the thermal plasma synthesis method is performed under an internal pressure condition of 0.2 bar to 3 bar in an inert argon gas or argon and hydrogen mixed gas atmosphere in order to produce a one-dimensional linear structure of FeCo nanochain. it is preferable When a reactive gas such as nitrogen is used instead of argon, a compound other than pure FeCo is generated, which can significantly lower absorption characteristics. When the pressure condition of 0.2 to 3 bar is exceeded, plasma is unstable and synthesis is difficult. There is this.

The manufacturing method of the present invention can manufacture a one-dimensional linear structure of FeCo nanochains by performing the manufacturing by the above method.

On the other hand, the manufacturing method of the present invention may further include the step of forming a dielectric inorganic coating layer on the surface of the FeCo nano-chain through the above steps, wherein the dielectric inorganic coating layer may be formed by various methods, It is possible to form a uniform coating layer and coating curing time according to the solvent concentration at a low temperature, and to achieve mass production, the process is not complicated, including drying of the solvent, and mass production is possible in a short time. It is preferable to be

In the present invention, the solution process means, for example, dispersing the FeCo nano-chains prepared in a mixed solvent of water and alcohol, introducing ammonia as a catalyst, and introducing TEOS to perform coating through a sol-gel process. In other words, since this is a known process, an additional detailed description will be omitted.

On the other hand, the weight ratio of iron and cobalt used as raw materials in the production method of the present invention is preferably 7:3 to 4:6. When the weight ratio of iron and cobalt is out of the above range, there is a problem in that the saturation magnetization value is lowered due to the low Co content, or the Co particles are separately formed because the Co content is too high.

The manufacturing method of the present invention can manufacture a one-dimensional linear structure of FeCo nanochains by a simple method, and since the manufactured FeCo nanochains have excellent electromagnetic wave absorption performance in a broad band, it can be applied to various application fields such as national defense.

Furthermore, the present invention provides an electromagnetic wave absorber comprising FeCo nano-chains in which a plurality of nanoparticles are fused to each other on the particle surface to form a one-dimensional linear structure, and each nanoparticle has a diameter of 30 nm to 500 nm.

The electromagnetic wave absorber of the present invention has a very simple manufacturing process, has a high surface area (surface area effect), and is a bulk material consisting of hundreds of millions of nanomaterial particles or more compared to the conventional electromagnetic wave absorber in the form of a nanorod, which is difficult to manufacture. Excellent optical and physical properties based on the expressed quantum size effect have advantages that can be expected as an electromagnetic wave absorber.

Hereinafter, the present invention will be described in more detail through experimental examples. However, the following experimental examples are only intended to specifically explain the present invention, and are not intended to limit the interpretation of the scope of the present invention by the following description.

Fabrication of FeCo Nanochains

The following experiment was performed to confirm whether a one-dimensional linear structure of FeCo nanochain was formed by the manufacturing method of the present invention.

In the case of using only iron powder as raw materials and iron and cobalt powder as raw materials, thermal plasma synthesis was performed under the following conditions, and the manufactured structure was confirmed by SEM (TSCAN (MIRA3 LM)), and the results are shown in FIG. indicated. FIG. 2 is an SEM photograph of a case where only Fe was used as a raw material and a Fe:Co ratio of 6:4 among the following experimental examples.

For the thermal plasma synthesis process, PL-35 equipment of TEKNA Plasma System of Canada was used, and argon gas was flowed at a flow rate of 80, 15, and 5 lpm as sheath gas, central gas, and carrier gas, respectively. Plasma was ignited under the condition of 2.5 kW and stabilized by increasing the output to 28 kW, and then, using a powder feeder, the raw material powder was injected into the thermal plasma formation area in the chamber together with the carrier gas at a feeding rate of 5 g/min. At this time, the raw material powder is CIP (carbonyl iron powder) powder (BASF) having an average particle size of 5 μm and pure Co powder having an average particle size of 1 μm in a weight ratio of 7:3, 6:4, 5:5, 4:6, It was prepared by mixing at a mixing ratio of 3:7. The mixed raw material powder injected into the thermal plasma chamber is vaporized while passing through a high-temperature thermal plasma region (>10000 K), and then, as it cools, nucleation and growth occur to form spherical FeCo nanoparticles, and then the nanoparticles collide. and sintered on the surface to form final FeCo nano-chain particles. The FeCo nanochains synthesized in the gas phase are finally collected by filtering by a metal filter in a collection chamber. In this experiment, FeCo nanochain particles were produced with a yield of about 30% by injecting raw materials at a condition of 5 g/min, and the thermal plasma synthesis process is a continuous process, so it can be continuously manufactured without a batch concept.

According to FIG. 2, when the process is performed using only iron as a raw material, a spherical result is formed, whereas when the process is performed using iron and cobalt as raw materials according to the manufacturing method of the present invention, the one-dimensional linear structure is actually formed. It can be seen that nanochains are formed.

Confirmation of the structure of FeCo nanochains

In order to more clearly confirm the structure of the prepared FeCo nanochain, the following experiment was performed.

The FeCo nanochain prepared in the process of Experimental Example 1 was confirmed by TEM, and the result is shown in FIG. 3 .

According to FIG. 3, it can be confirmed that, in fact, it has a one-dimensional linear structure, which is a FeCo nanochain manufactured by the manufacturing method of the present invention.

Confirmation of changes in nanochain structure according to composition

The following experiment was performed to confirm whether the structure of the nanochain was changed according to the composition ratio of the raw material.

FeCo nanochains were prepared in the same manner as in Experimental Example 1, but FeCo nanochains were prepared by changing the weight ratio of iron powder and cobalt powder to 3:7, 4:6, 5:5, 7:3, and as a result, was confirmed by SEM (TSCAN (MIRA3 LM)) and shown in FIG. 4 .

According to FIG. 4 , it can be confirmed that the manufactured nanochain still maintains a one-dimensional linear structure even when the weight ratio of iron and cobalt is changed in the range of 3:7 to 7:3.

Confirmation of dielectric constant and permeability characteristics according to composition ratio

In order to confirm the dielectric constant and magnetic permeability according to the composition ratio of the FeCo nanochain to be manufactured, the following experiment was performed.

For the nanochain by composition prepared in the same manner as in Experimental Example 1, the specimen prepared by stirring at a weight ratio of 1:1 with an epoxy resin and curing it at 180°C for 3 hours was tested using a Keysight 85051B coaxial tube and a Keysight N5222B Network Analyzer. After measuring the scattering coefficient by the coaxial tube method, the dielectric constant and the magnetic permeability were confirmed using the Keysight N1500A software, and the results are shown in FIG. 5 .

According to FIG. 5, it can be confirmed that the real part of the permittivity of the nanochain manufactured by the method according to the present invention is 10 or more, the real part of the permeability is 1.5, and the imaginary part is excellent at the level of 0.5.

Comparison of permittivity and permeability

In order to compare the dielectric constant and permeability of the FeCo nanochain according to the present invention with those of conventional electromagnetic wave absorber materials, the following experiment was performed.

Each material and the epoxy resin were stirred at a weight ratio of 1:1, and then cured at 180° C. for 3 hours to prepare a specimen for measuring dielectric constant/permeability. The FeCo nanochain was prepared by the method in which the Fe:Co weight ratio was 6:4 in the method of Experimental Example 1, and the existing materials used for comparison are as follows: BASF's carbonyl iron powder (model name EW), BASF Carbonyl iron powder (model name SQ) of the company, a nanopowder of the EW itself (CIP EW nanopowder), FeCo micropowder having an average particle diameter of 3.8 micrometers prepared by manufacturing an FeCo ingot and gas spraying. After measuring the scattering coefficient by coaxial tube method using Keysight 85051B coaxial tube and Keysight N5222B Network Analyzer, the dielectric constant and permeability were confirmed using Keysight N1500A software.

The results of the experiment are shown in FIG. 6 . According to FIG. 6 , it can be confirmed that the FeCo nanochain according to the present invention has remarkably excellent dielectric constant and magnetic permeability compared to conventional electromagnetic wave absorber materials.

Identification of surface dielectric layer coating

The following experiment was performed to confirm whether the dielectric layer was actually coated on the surface of the FeCo nanochain prepared by the method of the present invention.

A known sol-gel process was used for the ceramic coating. A TEOS solution was mixed with ethanol, and an aqueous ammonia (NH ₄ OH) solution was mixed with distilled water, respectively, and stirred at 60° C. for 15 minutes. After mixing the two solutions, FeCo nanochains prepared in an Fe:Co ratio of 6:4 in Experimental Example 1 were introduced into the mixed solution, and while stirring at room temperature for 45 minutes, coating the surface dielectric layer through hydrolysis reaction was performed. Thereafter, the coated nanochain was separated from the solution, and it was completely dried at a temperature of 70° C. in a vacuum chamber.

The nanochain dried by the above method was confirmed by TEM equipment, and the results are shown in FIG. 7 .

According to FIG. 7 , it can be confirmed that the silica coating layer is soundly formed on the surface of the actual FeCo nanochain.

Electromagnetic wave absorber manufacturing and evaluation

When the electromagnetic wave absorber was manufactured using the FeCo nanochain of the present invention, the following experiment was performed to evaluate its performance.

Fabrication of the specimen and measurement of permittivity and permeability were performed in the same manner as in Experimental Example 5. After attaching a copper tape, which is a perfect conductor (PEC), to the back of the prepared specimen, the absorption performance was confirmed by measuring the scattering coefficient using the Keysight 85051B coaxial tube and the Keysight N5222B Network Analyzer using the coaxial tube method.

The results of the above experiments are shown in FIGS. 8 to 11 . 8 to 11, it can be confirmed that the electromagnetic wave absorber including the FeCo nanochain of the present invention has excellent electromagnetic wave absorption performance in a wider band compared to existing materials, and thus, the FeCo nanochain of the present invention When used as this electromagnetic wave absorber, it can be confirmed that it has significantly superior performance than existing materials.

Claims

A plurality of nanoparticles are fused to each other on the particle surface to form a one-dimensional linear structure, and each nanoparticle has a diameter of 30 nm to 500 nm.
The FeCo nanochain according to claim 1, wherein the aspect ratio of the FeCo nanochain is 1.5 to 15.
The FeCo nanochain according to claim 1, wherein the FeCo nanochain further comprises a dielectric inorganic coating on the surface.
The FeCo nanochain according to claim 3, wherein the dielectric inorganic coating is a silica coating.
The FeCo nanochain according to claim 3, wherein the dielectric inorganic coating has a thickness of 2 nm to 200 nm.
The FeCo nanochain according to claim 1, wherein the FeCo nanochain is used as an electromagnetic wave absorber.
introducing a mixed powder of iron and cobalt or an alloy powder of iron and cobalt into the plasma region; and

Forming FeCo nanochains through thermal plasma synthesis; Method for producing FeCo nanochains having a one-dimensional linear structure, comprising: a.
The method of claim 7, wherein the thermal plasma synthesis method is performed in an inert argon gas atmosphere or an argon and hydrogen mixed gas atmosphere, at a chamber pressure of 0.2 to 3 bar. .
The method of claim 7, wherein the method further comprises forming a dielectric inorganic coating layer on the surface of the FeCo nanochain after forming the FeCo nanochain.
[10] The method of claim 9, wherein the forming of the inorganic dielectric coating layer is performed by a solution process.
[10] The method of claim 9, wherein the dielectric inorganic coating layer is formed of silica.
[10] The method of claim 9, wherein the dielectric inorganic coating layer is formed to a thickness of 2 nm to 200 nm.
The method of claim 7, wherein the weight ratio of iron and cobalt is 7:3 to 4:6.
An electromagnetic wave absorber comprising FeCo nano-chains in which a plurality of nanoparticles are fused to each other on the particle surface to form a one-dimensional linear structure, and each nanoparticle has a diameter of 30 nm to 500 nm.